Available evidence from pre-clinical and clinical studies indicates that adult autologous stem cell based therapies show modest improvement of cardiac function. Emerging evidence from preclinical studies also suggests that hostile micro-environment in the infarcted myocardium, including inflammation and oxidative damage, have adverse effects on transplanted stem cell survival and function thereby posing a significant barrier to the adult stem cell-based therapies for repair of injured myocardium. Therefore, novel approaches to enhance full functional benefits of stem cell based therapies are critically needed. Therefore use of cell-free components derived from stem cells including need to be explored for their reparative potential. Exosomes derived from number of stem cells may provide one such cell-free source. Exosomes, known regulators of intercellular communication, carry the cell specific mRNA/miRNA signature and participate in cell-cell communication by transferring their materials to the target cells. However, both the content and function of the exosome, even from the same cell source, may differ in context of cellular stresses such as diabetes and inflammation, known co-morbid factors in heart disease patients, a hypothesis supported by our key preliminary data on endothelial progenitor cell (EPC) exosomes. Our central hypothesis is that stress conditions of inflammation and hyperglycemia suppress reparative properties of EPC/stem cell exosomes and this loss of function is dependent upon stimulus-specific modifications in the exosomal miRNA/protein contents and their delivery to target cell/tissue. We will test our central hypothesis by conducting experiments organized under following 3 specific aims: 1) Elucidate stimulus-mediated impairment in myocardial reparative ability of EPC-derived exosomes in ischemic myocardial repair and identify the molecular determinants for exosome dysfunction; 2) To establish the role of selected microRNAs and signaling proteins as determinants of exosome dysfunction in response to stress stimuli and determine if their modulation rescues exosome phenotype; and 3) To determine the therapeutic potential of Human CD34 derived exosomes for post injury myocardial repair in clinically relevant large animal (swine) model of ischemia-reperfusion. The significance of this study is to develop a novel understanding of the role played by stem cell/EPC exosomes in supporting endogenous reparative processes in the heart. We will also extend these studies to determine the contribution of stimulus-specific miRNAs in regulating EPC-exosome reparative response to pathologic injury. Establishing the therapeutic value of these exosomes would help develop a novel cell free system to enhance myocardial repair and would provide a new direction for the restoration and/or augmentation of endogenous myocardial repair process.